Pyroacoustic transducer



v ELECTRICAL Jan. 23, 1968 J. 5. ARNOLD 3,365,552

PYROACOUSTIC TRANSDUCER Filed Jan. 27, 1966 To VciicE COIL 50L! RCE OF ELECTRICAL 3 l GNALS 50l/H2CE OF COMBUSTIBLE TO VOKLE COIL Ttpz 5OUQCE OF 5- 26 SIGNALS 50 U 126E OF I COMBU STI BLE INVENTOR 6% I JAM/15$ 5. ARA/01D /M Y W United States Patent Ofific e 3,365,552 Patented Jan. 23, 1968 3,365,552 PYROACOUSTIC TRANSDUCER James S. Arnold, Palo Alto, Caiifl, assignor to Stanford Research Institute, Menlo Park, Calif., a corporation of California Filed Jan. 27, 1%6, Ser. No. 523,331 6 Claims. (Cl. 179-108) This invention relates to loudspeakers of the type e-rnploying gas flow, and more particularly to a method and means for increasing the acoustical output of such loudspeakers.

In an application by this inventor entitled, Thermoacoustic Loudspeaker, Ser. No. 424,414, filed Jan. 8, 1965, there is described and claimed a pyroacoustic transducer of the type wherein a flow of combustible gas is modulated in accordance with signal information by means such as the diaphragm of the speaker. This adds energy from the combustion to the sonic energy which results in the production of a higher sound intensity than would be obtained in the absence of combustion.

An object of this invention is to provide an improved pyroacoustic transducer whereby the gas is simultaneously burned and modulated.

Still another object of the present invention is the provision of a novel and unique arrangement for a pyroacoustic transducer.

Yet another object of the present invention is the provision of a pyroacoustic transducer having an improved efliciency.

These and other objects of the present invention are achieved in a structural arrangement for a pyroacoustic transducer comprising the usual speaker, magnet and voice coil structure where, however, the diaphragm is omitted and the cylindrical voice coil bobbin is coupled to drive a wire gauze flame holder. Combustible gas under substantially constant pressure is fed to the rear side of the wire gauze through which it passes and at which it is ignited. When an electrical signal is applied to the voice coil, axial motion of the voice coil, the bobbin on which it is wound and the flame holder is produced. Motion of the flame holder causes modulation of the flow velocity through it even though the gas input rate to the transducer is constant. This in turn causes a modulation of the chemical reaction rate at the flame and a large acoustic output at the frequency of the signal that drives the voice coil results.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of ope-ration, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a schematic cross-sectional view of an embodiment of the invention; and

FIGURE 2 is a schematic cross-sectional view showing a modification of the embodiment of the invention shown in FIGURE 1.

FIGURE 1 shows a schematic, cross-sectional view of the invention which comprises a magnetic structure 10 of the kind used for a loudspeaker. This has the usual circular slot 12 into which a voice coil 14 which is attached to a bobbin 16 is inserted. The bobbin is supported on the outside by the usual resilient bobbin supporting material 18. This material is usually attached, as by rivets 20, to the top of the magnet 10 with the inner surface thereof being glued to the side of the bobbin. Material providing a gas seal 22 is glued to the inner surface of the bobbin and to the magnet 10 in order to prevent gas which is supplied to the area defined by the bobbin from escaping through the slot 12. This material may be made of the same material as is employed for the bobbin support if it is sufliciently dense to prevent gas leaking therethrough. Otherwise, any suitable resilient material may be employed.

The end of the bobbin 16 is covered with a wire gauze material 24, suitable for use as the flame holder. The wire gauze may be mechanically attached to the bobbin by any suitable means, such as epoxy or staples, etc. An opening 26 extending through the magnet 10 is used to conduct gas from a source of combustible gas 28 through this opening into the region confined by the bobbin and the wire gauze. A suitable orifice is established at the end of the opening 26 by inserting therein a washer 30.

Signals from a source of electrical signals 32 are connected to the voice coil. The combustible gas is ignited outside the wire gauze, which acts as a flame holder. The signals applied to the voice coil causes axial motion of the voice coil, bobbin and flame holder. The motion of the flame holder causes modulation of the flow velocity through it, although the gas input rate to the transducer is constant. A proper choice of the gas mixture and flow rate enables the flame to attach to the moving flame holder, thus causing modulation of the chemical reaction rate and a large acoustic output having the modulation of the signal that drives the voice coil. If the pressure from the source is properly chosen, the pressure and flow fluctuation caused by the vibrating wire gauze has no effect on the gas flow rate.

FIGURE 2 shows a modification of FIGURE 1 which may be employed if it is to place the flame farther away from the bobbin and voice coil to avoid adverse effects due to the heat of the flame or because it may be desirable to provide a larger flame area. Structures in FIG- URE 2 which function similar to structures in FIGURE 1 have the same reference numerals applied thereto. It will thus be seen that the modification comprises supporting the flame holder Wire gauze ,0, by means of a cylindrical support 42, which is glued or attached by rivets, to the top of the magnet 10. The bobbin has a metal strip 4 laid across it and attached to it. A rod 46, which is connected to both wire gauze and strip serves to vibrate the voice coil with the vibration imparted to it from the bobbin. The combustible gas which passes through the wire gauze is spread over a larger area and when ignited the flame extends over a larger area. The operation is the same as is described in connection with FIGURE 1.

From the foregoing description, it will be seen that a novel, improved and more eflicient pyroacoustic transducer has been described. The vibrating gauze constitutes less of a mechanical load on the driving system than does a vibrating diaphragm and thus can produce a greater audio modulation for substantially the same electrical input.

What is claimed is:

1. A pyro-acoustic transducer comprising a flame supporting member having a plurality of openings therethrough, a source of combustible gas, means for applying gas to one side of said flame supporting member to cause it to pass through the openings therethrough to the other side, a source of electrical signals, and means for vibrating said flame supporting member responsive to signals from said electrical source whereby combustion of said combustible gas at the other side of said flame supporting member produces an acoustic output representative of said electrical signal.

2. A pyroacoustic transducer as recited in claim 1 wherein said means for vibrating said flame supporting member comprises a bobbin, means for attaching said flame supporting member to said bobbin to vibrate therewith, a loudspeaker voice coil wound on said bobbin,

means for establishing a magnetic field transverse to the axis of said voice coil, and means for applying electrical signals from said source of electrical signals to said voice coil.

3. A pyroacoustic transducer as recited in claim 2 wherein said flame supporting means comprises a wire gauze, and said means for attaching said flame supporting means to said bobbin attaches it directly to the end of said bobbin.

4-. A pyroacoustic transducer as recited in claim 2 wherein said flame supporting member is a wire gauze, there is included a means for supporting said wire gauze adjacent an end of said bobbin, and said means for attaching said flame supporting means to said bobbin includes a rod means attached to said bobbin and to said wire gauze when said bobbin is vibrated.

5. A pyroacoustic transducer comprising a cylindrical bobbin, the center of said bobbin being open, a wire gauze extending over the opening at one end of said bobbin, means for attaching said wire gauze to said bobbin, a voice coil wound around said bobbin toward its other end, a magnet having a circular slot therein, resilient means for supporting said bobbin with its voice coil in the circular slot of said magnet, a source of combustible gas, an opening through said magnet for permitting the introduction of combustible gas from said source into the central opening of said bobbin whereby it blows through said wire gauze, a source of electrical signals, means for applying electrical signals from said source to said voice coil to cause vibration of said voice coil, said bobbin and said wire gauze responsive thereto whereby ignition of said combustible gas at said wire gauze produces an acoustic output representative of the electrical signals.

6. A method of producing an acoustic output representative of electrical signals comprising applying a combustible gas to one side of a porous flame holder, igniting said combustible gas at the other side of said porous flame holder, and vibrating said porous flame holder responsive to electrical signals of said source whereby an acoustic output is produced.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner. 

6. A METHOD OF PRODUCING AN ACOUSTIC OUTPUT REPRESENTATIVE OF ELECTRICAL SIGNALS COMPRISING APPLYING A COMBUSTIBLE GAS TO ONE SIDE OF A POROUS FLAME HOLDER, IGNITING SAID COMBUSTIBLE GAS AT THE OTHER SIDE OF SAID POROUS FLAME HOLDER, AND VIBRATING SAID POROUS FLAME HOLDER RESPONSIVE TO ELECTRICAL SIGNALS OF SAID SOURCE WHEREBY AN ACOUSTIC OUTPUT IS PRODUCED. 